This invention relates to a refrigerator equipped with a two-stage compressor and two evaporators for performing a refrigeration cycle.
Such a refrigerator has been proposed and described in U.S. Pat. No. 4,918,942.
The refrigeration cycle of the prior art document comprises following steps; each of the steps will be explained by referring FIG. 9, which shows a refrigerant circuit 22xe2x80x2.
(1) Gaseous refrigerant streams out at high pressure from an outlet of the two-stage compressor 18. Then, the gaseous refrigerant is condensed at interior of a condenser 18 to become a two-phase refrigerant composed of gas and liquid phases at high pressure.
(2) The two-phase refrigerant at high pressure is subjected to pressure reduction in a capillary tube 50. Then, the two-phase refrigerant at intermediate pressure flows into an evaporator 10 for fresh food compartments or non-freezing refrigerator compartment (hereinafter referred as xe2x80x9cfresh food evaporatorxe2x80x9d).
(3) Liquid-phase part of the two-phase refrigerant partly evaporates at inside of the fresh food evaporator 10. Then, the two-phase refrigerant enters into a separator 28, through which gas-phase and liquid-phase parts are separated from each other. A fan 12 disposed near the fresh food evaporator 10 sends an air cooled by the evaporator 10, into the fresh food compartment.
(4) Gaseous refrigerant that is separated from liquid refrigerant by the separator 28 flows through a suction pipe 30 at intermediate pressure; and then returns to the two-stage compressor 18 through its intermediate-pressure side inlet.
(5) Liquid refrigerant that is separated from the gaseous refrigerant by the separator 28 is subjected to pressure reduction at a capillry tube 32, to form a two-phase refrigerant at low pressure. Then, the two-phase refrigerant at low pressure flows into an evaporator 14 for freezer compartment (hereinafter referred as xe2x80x9cfreezer evaporatorxe2x80x9d).
(6) Liquid part of the two-phase refrigerant evaporates in the freezer evaporator 14. Thus formed gaseous refrigerant flows through a suction pipe 34 at low pressure; and then returns to the two-stage compressor 18 through its low-pressure side inlet.
In the refrigerant circuit 22xe2x80x2, diameter and length of the capillary tubes 50, 32 are invariant; and hence extents of throttling or refrigerant passages in the throttlers are invariant. Hence, when operational power of the compressor 18 increases, that is, when operational frequency of the compressor 18 increases, circulating rate of refrigerant increases; and thereby, pressure reduction at the capillary tubes 50, 32 increases due to increased effect of the throttler.
When inside of the freezer compartment is not cool enough, operational control of the refrigerator is made such as to increase drive frequency of the two-stage compressor 18 for sake of cooling the inside of the freezer compartment; even if inside of the fresh food compartment has been sufficiently cooled. Since the fresh food evaporator is located upstream of the freezer evaporator, temperature dropping in the fresh food evaporator is followed by that in the freezer evaporator. Because temperature drops in both of the fresh food and freezer evaporators, cooling power of the refrigerator is enhanced. Nevertheless, cooling power becomes excessive for the fresh food compartment; thus, it is necessary either dropping down the airflow rate of the fan 12 for the fresh food compartment or stopping of the fan 12.
Such stopping of the fan 12 or dropping down of the air-flow rate may cause insufficient evaporation within the fresh food evaporator, and thereby cause xe2x80x9coverflowxe2x80x9d of liquid refrigerant at inside of the gas-liquid separator 28; making the liquid refrigerant return to the two-stage compressor 18 through the intermediate-pressure suction pipe 30. Thus, stability or operational safety or stability of the refrigerant circuit 22xe2x80x2 is damaged.
First aspect of invention-wise refrigerator comprising: a two-stage compressor having an outlet and first and second inlets, pressure of said first inlet being intermediate between pressures of the outlet at higher pressure and the second inlet at lower pressure; a condenser at downstream of said outlet; a first evaporator at downstream of the condenser; a gas-liquid separator being at downstream of the first evaporator and having a gas-phase refrigerant exit and a liquid-phase refrigerant exit; a second evaporator at downstream of said liquid-phase refrigerant exit; a first suction pipe connecting from the gas-phase refrigerant exit to said first inlet of the compressor; a second suction pipe connecting from the second evaporator to said second inlet of the two-stage compressor; a first fan for sending out air around the first evaporator into a fresh food compartment; a second fan for sending out air around the second evaporator into a freezer compartment; first and second throttlers, respectively interposed between the condenser and the first evaporator, and between said liquid-phase refrigerant exit and the second evaporator, throttling extent of at least one of said first and second throttlers being variable in response of computerized control; sensors for detecting temperatures in the fresh food and freezer compartments and in the first and second evaporators; and controller for controlling power of the compressor and throttling extent of said at least one of the first and second throttlers, based on detection of said sensors, as to keep said temperatures within respective prescribed ranges.
Preferably, throttling extent of said first throttler is varible and controlled by the controller. Alternatively, throttling extent of said second throttler is varible and controlled by the controller. In a more prefered manner, throttling extent of said first and second throttlers being varible and controlled by the controller.
Temperature in the first evaporator is preferably controlled within a prescribed temperature range so that surface temperature of the first evaporator being controlled substantially at 0xc2x0 C. or more. The prescribed temperature range may be from xe2x88x922xc2x0 C. to 2xc2x0 C. in typical situation.
By such controlling, water on the first evaporator for the fresh food compartment is kept in liquid phase. Thus, although moisture of taken-in air deposited on the evaporator, evaporation therefrom also takes place; and thereby, high humidity in the fresh food compartment is ensured.
According to second aspect of the invention, said refrigerator further comprising a sensor for detecting temperature ambient to the refrigerator; and said controller determining whether such ambient temperature is higher than a prescribed upper limit; and, if so determined, implementing an operational control for coping with such high ambient temperature, in that the first evaporator is kept at substantially lowest of said prescribed temperature range, by controlling said extent of throttling.
By such features, temperature of the first evaporator is kept in ice-free range; and in same time, cooling power of the refrigerator is kept high as to achieve sufficient food preservation in the fresh food compartment, even when the ambient temperature is high.
According to third aspect of the invention, in said refrigerator, said controller implementing an operational control comprising (1)-(3) in following:
(1) determining whether vigorous cooling is needed for the freezer compartment;
(2) reducing temperature in the first evaporator, if so determined, to said prescribed temperature range, by keeping power of the compressor as enhanced to substantially its maximum; while keeping rotational numbers of the first and second fans as raised above their predominant operation range, and by keeping the throttling extent of the first throttler as intense; and then,
(3) reducing temperature of the second evaporator to a temperature for the vigorous cooling, while allowing temperature rise in the first evaporator, by further keeping power of the compressor as enhanced to substantially its maximum and by keeping rotational number of the first fan as reduced below its predominant operation range; while keeping rotational number of the second fan as raised above its predominant operation range, and by keeping the throttling extent of the first throttler as intense.
By such construction, the vigorous cooling for the freezer compartment is made and in same time, humidity in the fresh food compartment is kept high.
According to fourth aspect of the invention, in said refrigerator, said controller implementing an operational control comprising (1)-(4) in following:
(1) determining the temperature ambient to the refrigerator to be lower than a prescribed lower limit;
(2) reducing temperature of the first evaporator, if so determined, to a temperature within said prescribed temperature range by keeping power of the compressor as reduced below its predominant operantion range; while rotational numbers of the first and second fans are reduced below their predominant operation range, and throttling extent of the first throttler is kept as loosen;
(3) subsequently, further reducing temperature in the second evaporator to a temperature within a presciribed range or within a predominant operation range of the second evaporator, by further keeping rotational number of the second fan as reduced below its predominant operation range; while stopping the first fan and keeping the throttling extent of the first throttler as intense; and
(4) when the temperature of the second evaporator having been reduced to its predominant operation range, making or keeping temperature in the first evaporator as to be ice free on its surface, by loosening the throttle extent of the first throttler substantially to its maximum; while keeping rotaitional number of the first fan within its predominant operation range, and while reducing the rotational number of or stopping the second fan.
In th above (4), preferably, the power of the compressor is further reduced or the compressor is stopped.
By these features, defrosting is made on surface of the first evaporator as to keep high humidity in the fresh food compartment, because refrigerant in sufficiently high temperature flows into the first evaporator.
The throttler that is vairble is preferably a variable valve. The variable valve may be either of a pulse motor valve and an electrical variable valve comprised of piezoelectric actuator